Influenza hemagglutinin-specific monoclonal antibodies for preventing and treating influenza virus infection

ABSTRACT

Disclosed herein are neutralizing antibodies with cross-neutralizing activity and cross-protective effects against divergent stains of influenza virus, which are specific for an epitope having at least 90% homology to amino acids +72-115 of the HA1 domain of H5N1 influenza virus hemagglutinin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) to U.S.Provisional Patent Application 61/405,100 filed Oct. 20, 2010, theentire contents of which are incorporated by reference herein.

FIELD

The present application is drawn to neutralizing monoclonal antibodiesfor preventing and treating influenza virus infection and methods oftreating influenza virus infection.

BACKGROUND

The Influenza A virus, which belongs to the Orthomyxoviridae family, cancause influenza in humans, birds or domesticated food animals. The viruscan be classified into different subtypes based on their surfaceglycoproteins, hemagglutinin (HA) and neuraminidase (NA). Of the 16known HAs and nine NAs, three HA subtypes (H1, H2, and H3) and two NAsubtypes (N1 and N2) are most commonly found in humans. H1N1 and H3N2are the major subtypes that cause human seasonal flu and globalpandemics of influenza. The influenza pandemic in 2009 was caused byinfluenza A virus H1N1 of swine origin. This has led to a growingconcern regarding the pandemic potential of the highly pathogenic avianinfluenza H5N1 viruses. Thus the development of an effective and safevaccine against divergent influenza A virus strains is urgently neededfor the prevention of future outbreaks of influenza.

Neutralizing monoclonal antibodies (MAbs), particularly those havingcross-clade neutralizing activity, play a critical role inimmunoprotection against various influenza A virus (IAV) infections,particularly those caused by the highly pathogenic avian influenza H5N1virus and any future unpredictable virus strains.

Although vaccination is an important strategy to prevent influenzainfection, most of the current vaccines cannot provide immediateprotection in the event of influenza pandemics and epidemics due to thelength of time required for producing effective vaccines. Furthermore,these vaccines are limited to one or just a few strains and don'tproduce highly potent neutralizing antibodies or cross-reactive immunityagainst divergent influenza viruses. Neutralizing antibodies can providea first line of defense against influenza pathogens and passiveimmunization with neutralizing MAbs can provide immediate effects toprevent the spread of influenza infection and mortality. However, it hasbeen difficult to obtain MAbs which neutralize divergent strains ofinfluenza viruses with sufficient cross-protective immunity.

SUMMARY

Disclosed herein are neutralizing monoclonal antibodies (MAbs) specificfor the surface hemagglutinin (HA) protein of the influenza H5N1 strain.The MAbs recognize the highly conserved HA1 region of H5N1 hemagglutininand inhibit multiple strains of the H5N1 virus, as well as treated miceinfected with a lethal dose of H5N1 viruses of two divergent strains,demonstrating their potential as therapeutic agents for multivalentprophylaxis and treatment of influenza. These two MAbs were proven toinhibit virus infection in the post-attachment process rather thaninhibition of receptor binding.

In one embodiment disclosed herein, a neutralizing antibody specific foran epitope having at least 90% homology to amino acids +72-115 of theHA1 domain of H5N1 influenza virus hemagglutinin is provided. In anotherembodiment, the neutralizing antibody is a monoclonal antibody such as amouse antibody, a humanized antibody, a chimeric antibody, or a fragmentthereof.

In another embodiment, the epitope has at least 95% or at least 98%homology to amino acids +72-115 of the HA1 domain of H5N1 influenzavirus hemagglutinin.

In yet another embodiment, the neutralizing antibody is produced byhybridoma HA-3 (ATCC accession number PTA-12174). In yet anotherembodiment, the neutralizing antibody is produced by hybridoma HA-7(ATCC accession number PTA-12173). Hybridomas HA-3 and HA-7 weredeposited with the American Type Culture Collection (ATCC), 10801University Blvd., Manassas, Va. 20110 under the provisions of theBudapest Treaty.

Also disclosed herein is a pharmaceutical formulation for neutralizinginfluenza virus comprising an antibody specific for an epitope having atleast 90% homology to amino acids +72-115 of the HA1 domain of H5N1influenza virus hemagglutinin.

Also disclosed herein is a method of treating influenza virus infectionin a subject in need thereof comprising administering a therapeuticallyeffective amount of the neutralizing antibody specific for an epitopehaving at least 90% homology to amino acids +72-115 of the HA1 domain ofH5N1 influenza virus hemagglutinin and thereby treating said influenzavirus infection in said subject.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the percentage of neutralization by HA-targeting MAbs ofH5N1 pseudovirus expressing HA of A/Xinjiang/1/2006 (XJ-HA), as measuredby pseudovirus neutralization assay. The dilution of the MAbs is 1:450.

FIG. 2 depicts the percentage of neutralization by HA-targeting MAbs ofH5N1 pseudovirus expressing A/Qinghai/59/05 (QH-HA), as measured bypseudovirus neutralization assay. The dilution of the MAbs is 1:450.

FIG. 3 depicts the percentage of neutralization by HA-targeting MAbs ofH5N1 pseudovirus expressing HA of A/Anhui/1/2005 (AH-HA), as measured bypseudovirus neutralization assay. The dilution of the MAbs is 1:450.

FIG. 4 depicts the percentage of neutralization by HA-targeting MAbs ofH5N1 pseudovirus expressing HA of A/Hong Kong/156/97 (HK-HA), asmeasured by pseudovirus neutralization assay. The dilution of the MAbsis 1:450.

FIG. 5 depicts the percentage of neutralization by HA-targeting MAbs ofH5N1 pseudovirus expressing HA of A/VietNam/1194/2004 (1194-HA), asmeasured by pseudovirus neutralization assay. The dilution of the MAbsis 1:450.

FIG. 6 depicts the percentage of neutralization by MAbs HA-3 and HA-7 attwo concentrations of H5N1 pseudovirus expressing HA of five differentstrains, as measured by pseudovirus neutralization assay.

FIG. 7 depicts the survival rate of MAbs HA-3- and HA-7-treated miceinfected with a lethal dose of A/VietNam/1194/2004 (VN/1194) H5N1 virus.The control mice were treated with a MAb targeting the receptor-bindingdomain (RBD) of severe acute respiratory syndrome coronavirus(SARS-CoV).

FIG. 8 depicts the survival rate of MAbs HA-3- and HA-7-treated miceinfected with a lethal dose of A/Shenzhen/406H/06 (SZ/406H) H5N1 virus.A MAb targeting the RBD of SARS-CoV was used as the control.

FIG. 9 depicts the body weight change of MAbs HA-3- and HA-7-treatedmice infected with lethal dose of VN/1194 H5N1 virus. A MAb targetingthe RBD of SARS-CoV was used as the control.

FIG. 10 depicts the body weight change of MAbs HA-3- and HA-7-treatedmice infected with lethal dose of SZ/406H H5N1 virus. A MAb targetingthe RBD of SARS-CoV was used as the control.

FIG. 11 depicts the quantification of viral RNA in H5N1 virus-infectedlung tissue of mice injected with MAbs HA-3 and HA-7 by quantitativereal-time PCR. A MAb targeting the RBD of SARS-CoV was used as thecontrol. The limit of detection was 1.5.

FIG. 12 depicts the ELISA detection of the reactivity of MAbs HA-3 andHA-7 with recombinant HA1 proteins respectively fused with the human Fcimmunoenhancer (HA1-hFc), trimeric Fd sequences (HA1-Fd), or the Fd plushFc (HA1-Fd-hFc), and HA1 protein without the hFc and Fd (HA1-His), aswell as recombinant hIgG1-Fc2 protein (hFc), commercial human IgG Fcprotein (IgG-Fc), Fd fused with HIV-1 gp41 (HIV-Fd), and SARS RBDprotein. The dilution of the antibody was 1:3200.

FIG. 13 depicts the reactivity of MAbs HA-3 and HA-7 with inactivatedinfluenza A viruses (IAVs), as measured by ELISA. The dilution of theantibody was 1:3200.

FIG. 14 depicts the detection of IgG subtypes of MAbs HA-3 and HA-7, asmeasured by ELISA, using recombinant HA1-His protein as the coatingantigen. The dilution of the antibody was 1:3200.

FIG. 15 depicts epitope mapping of the MAbs HA-3 and HA-7, as measuredby ELISA on plates coated with truncated recombinant HA1 proteinfragments comprising the indicated portions of the HA1 region. Thedilution of the antibody was 1:3200.

FIG. 16 depicts the reactivity of MAbs HA-3 and HA-7 with overlappingpeptides covering the full-length HA protein of A/Anhui/1/2005(H5N1), asmeasured by ELISA. The dilution of the antibody was 1:3200.

FIG. 17 depicts the reactivity of MAbs HA-3 and HA-7 with DTT-denaturedrecombinant HA1 proteins of different lengths, with the native HA1proteins without DTT treatment as a comparison. The dilution of theantibody was 1:51200.

FIG. 18 depicts the binding of MAbs HA-3 and HA-7 to H5N1 pseudovirus,as measured by virus binding assay using QH-HA pseudovirus invirus-infected MDCK cells.

FIG. 19 depicts the binding of MAb HA-3 to H5N1 pseudovirus, as measuredby post-attachment assay using QH-HA pseudovirus in virus-infected MDCKcells.

FIG. 20 depicts the binding of MAb HA-7 to H5N1 pseudovirus, as measuredby post-attachment assay using QH-HA pseudovirus in virus-infected MDCKcells.

DETAILED DESCRIPTION

Development of universal neutralizing monoclonal antibodies (MAbs) withcross-protective immunity is crucial to prevent and treat influenzapandemics and epidemics caused by divergent strains of influenza A virus(IAV). Disclosed herein are protective neutralizing MAbs specific to thehemagglutinin (HA) protein (SEQ ID NO. 1)_of the H5N1 virus produced byimmunizing mice with a recombinant protein encoding HA1 (SEQ ID NO. 2)of the A/Anhui/1/2005 (H5N1) strain fused with the trimeric motif foldon(Fd) (SEQ ID NO. 3) and the Fc portion of human IgG1 (SEQ ID NO. 4). Twoof these MAbs (HA-3 and HA-7) have highly potent cross-neutralizingactivity that neutralized infections with at least five strains of H5N1pseudovirus expressing HA proteins, including homologous A/Anhui/1/2005(AH-HA) and heterologous A/Xinjiang/1/2006 (XJ-HA), A/Qinghai/59/05(QH-HA), A/Hong Kong/156/97 (HK-HA) and A/VietNam/1194/2004 (1194-HA) ina cell culture-based neutralization assay. ELISA-based epitope mappinganalysis indicated that the neutralizing MAbs targeted the N-terminal ofthe HA1 region of H5N1 HA, a highly conserved region with >90% homologyamong hundreds of identified H5N1 isolates that cause human andnon-human infections. These results indicate that the MAbs arepotentially significant immunotherapeutics for prevention or treatmentof IAV infections, particularly those caused by the highly pathogenicH5N1 virus.

Annually-occurring epidemics and pandemics caused by IAVs have claimedmillions of lives worldwide. This has been seen most recently in theglobal outbreak of swine-origin influenza virus (S-OIV) H1N1 in 2009.Furthermore, the increasing number of influenza cases caused by thehighly pathogenic avian influenza virus H5N1 makes it particularlyimportant to develop effective preventative and immunotherapeuticmeasures against divergent IAVs, particularly avian H5N1. Among variousantiviral agents, neutralizing MAbs are considered an essential passiveimmunotherapeutic having an immediate effect against influenza virusinfection. Disclosed herein are two novel neutralizing MAbs targetingthe highly conserved HA1 region of the HA protein of H5N1.

In embodiments disclosed herein, the HA sequences refer to HA or HA1sequences of the following influenza viruses H5N1, H1N1, H3N2, H9N2 andthe H1, H2, H3, H5, H7 and H9 strains.

Additionally, within the scope of the instant disclosure are chimeric,or antibody fragments with specificity for the epitope having 80%, 85%,90%, 92%, 95%, 97%, 98%, 99% or 100% homology to amino acids +72-115(SEQ ID NO. 15) of the influenza H5N1 virus HA1 domain and having virusneutralizing activity. In one embodiment, the monoclonal antibodies areantibodies HA-3 (produced by hybridoma HA-3 having ATCC accession numberPTA-12174) and HA-7 (produced by hybridoma HA-7 having ATCC accessionnumber PTA-12173). Hybridomas HA-3 and HA-7 were deposited with theAmerican Type Culture Collection (ATCC), 10801 University Blvd.,Manassas, Va. 20110 under the provisions of the Budapest Treaty.

TABLE 1 Amino acid sequences SEQ ID NO. 1 [A/Anhui/1/2005(H5N1) HA]:MEKIVLLLAIVSLVKSDQICIGYHANNSTEQVDTIMEKNVTVTHAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKGDSAIVKSEVEYGNCNTKCQTPIGAINSSMPFHNIHPLTIGECPKYVKSNKLVLATGLRNSPLRERRRKRGLFGAIAGFIEGGWQGMVDGWYGYHHSNEQGSGYAADKESTQKAIDGVTNKVNSIIDKMNTQFEAVGREFNNLERRIENLNKKMEDGFLDVWTYNAELLVLMENERTLDFHDSNVKNLYDKVRLQLRDNAKELGNGCFEFYHKCDNECMESVRNGTYDYPQYSEEARLKREEISGVKLESIGTYQILSIYSTVASSLALAIMVAGLSLWMCSNGSLQCRICISEQ ID NO. 2 [A/Anhui/1/2005(H5N1) HA1 +3-322]:ICIGYHANNSTEQVDTIMEKNVTVTHAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKGDSAIVKSEVEYGNCNTKCQTPIGAINSSMPFHNIHPLTIGECPKYVKSNKLVLATGLRNSPLSEQ ID NO. 3 [Foldon (Fd)]: GYIPEAPRDGQAYVRKDGEWVLLSTFLSEQ ID NO. 4 [human IgG Fc (hFc)]:RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKSEQ ID NO. 5 [A/Anhui/1/2005(H5N1) HA1(+3-322)-Fd-hFc]:ICIGYHANNSTEQVDTIMEKNVTVTHAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKGDSAIVKSEVEYGNCNTKCQTPIGAINSSMPFHNIHPLTIGECPKYVKSNKLVLATGLRNSPL-GYIPEAPRDGQAYVRKDGEWVLLSTFL-RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSP GKSEQ ID NO. 6 [A/Anhui/1/2005(H5N1) HA1(+3-322)-hFc]:ICIGYHANNSTEQVDTIMEKNVTVTHAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKGDSAIVKSEVEYGNCNTKCQTPIGAINSSMPFHNIHPLTIGECPKYVKSNKLVLATGLRNSPL-RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNVVYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKSEQ ID NO. 7 [A/Anhui/1/2005(H5N1) HA1(+3-322)-Fd]:ICIGYHANNSTEQVDTIMEKNVTVTHAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKGDSAIVKSEVEYGNCNTKCQTPIGAINSSMPFHNIHPLTIGECPKYVKSNKLVLATGLRNSPL-GYIPEAPRDGQAYVRKDGEWVLLSTFLSEQ ID NO. 8 [A/Anhui/1/2005(H5N1) HA1(+3-322)-His]:ICIGYHANNSTEQVDTIMEKNVTVTHAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKGDSAIVKSEVEYGNCNTKCQTPIGAINSSMPFHNIHPLTIGECPKYVKSNKLVLATGLRNSPL-HHH HHHSEQ ID NO. 9 [A/Anhui/1/2005(H5N1) HA1 +105-322]:LSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKGDSAIVKSEVEYGNCNTKCQTPIGAINSSMPFHNIHPLTIGECPKYVKSNKLVLATGLRNSPLSEQ ID NO. 10 [A/Anhui/1/2005(H5N1) HA1 +105-259]:LSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKSEQ ID NO. 11 [A/Anhui/1/2005(H5N1) HA1 +3-259]:ICIGYHANNSTEQVDTIMEKNVTVTHAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKSEQ ID NO. 12 [A/Anhui/1/2005(H5N1) HA1 +28-259]:HAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKSEQ ID NO. 13 [A/Anhui/1/2005(H5N1) HA1 +45-259]:DGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKSEQ ID NO. 14 [A/Anhui/1/2005(H5N1) HA1 +72-259]:NVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKSEQ ID NO. 15 [A/Anhui/1/2005(H5N1) HA1 +72-115]:NVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQSEQ ID NO. 16 [A/Anhui/1/2005(H5N1) HA1(+105-322)-Fd-hFc]:LSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKKGDSAIVKSEVEYGNCNTKCQTPIGAINSSMPFHNIHPLTIGECPKYVKSNKLVLATGLRNSPL-GYIPEAPRDGQAYVRKDGEWVLLSTFL-RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSN KALPAPI EKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKSEQ ID NO. 17 [A/Anhui/1/2005(H5N1) HA1(+105-259)-Fd-hFc]:LSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKK-GYIPEAPRDGQAYVRKDGEWVLLSTFL-RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKSEQ ID NO. 18 [A/Anhui/1/2005(H5N1) HA1(+3-259)-Fd-hFc]:ICIGYHANNSTEQVDTIMEKNVTVTHAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKK-GYIPEAPRDGQAYVRKDGEWVLLSTFL-RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSL SLSPGKSEQ ID NO. 19 [A/Anhui/1/2005(H5N1) HA1(+28-259)-Fd-hFc]:HAQDILEKTHNGKLCDLDGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKK-GYIPEAPRDGQAYVRKDGEWVLLSTFL-RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKSEQ ID NO. 20 [A/Anhui/1/2005(H5N1) HA1(+45-259)-Fd-hFc]:DGVKPLILRDCSVAGWLLGNPMCDEFINVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKK-GYIPEAPRDGQAYVRKDGEWVLLSTFL-RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNVVYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKSEQ ID NO. 21 [A/Anhui/1/2005(H5N1) HA1(+72-259)-Fd-hFc]:NVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQIIPKSSWSDHEASSGVSSACPYQGTPSFFRNVVWLIKKNNTYPTIKRSYNNTNQEDLLILWGIHHSNDAAEQTKLYQNPTTYISVGTSTLNQRLVPKIATRSKVNGQNGRMDFFWTILKPNDAINFESNGNFIAPEYAYKIVKK-GYIPEAPRDGQAYVRKDGEWVLLSTFL-RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPG KSEQ ID NO. 22 [A/Anhui/1/2005(H5N1) HA1(+72-115)-Fd-hFc]:NVPEWSYIVEKANPANDLCYPGNFNDYEELKHLLSRINHFEKIQ-GYIPEAPRDGQAYVRKDGEWVLLSTFL-RSDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSREEMTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK

For the generation of MAbs specific to HA1, BALB/c mice weresubcutaneously immunized with a recombinant HA1-Fd-hFc protein (SEQ IDNO. 5) which comprised HA1 (residues +3-322 of H5N1 HA[A/Anhui/1/2005(H5N1)]) fused with a trimeric Fd sequence and an Fcimmunoenhancer sequence (Fc of human IgG) for four weeks at 2 weekintervals. Two MAbs exhibiting neutralizing activity (HA-3 and HA-7)were tested for passive protective immunity against two divergentstrains of H5N1 virus. In addition, the MAbs were assayed by ELISA forspecificity using recombinant HA1 proteins fused with Fd and hFc(HA1-Fd-hFc), Fd (HA1-Fd), hFc (HA1-hFc) or HA1 without Fd and Fc(HA1-His), and using recombinant human IgG1-Fc (hFc), commercial humanIgG-Fc (IgG-Fc), Fd protein fused with HIV-gp41 (HIV-Fd), or SARS RBDprotein as controls. These two MAbs were further tested by ELISA forreactivity with recombinant proteins containing different portions ofthe HA1 fusion protein (HA1-Fd-hFc) to determine the potential bindingsites and map the epitopes of the MAbs. Furthermore, overlappingpeptides covering the full-length HA protein of A/Anhui/1/2005(H5N1)were also used as the targets for the epitope mapping of the MAbs, aswell as detection of the conformation of the MAbs. Additionally, themechanism of these two neutralizing MAbs was further analyzed usingvirus binding and post-attachment assays.

Two of the 25 antibodies, designated HA-3 and HA-7, contained hightiters of neutralizing activity that neutralized not only the homologousAH-HA strain but also heterologous H5N1 strains of XJ-HA, QH-HA, HK-HAand 1194-HA. Both MAbs were able to completely protect vaccinated miceagainst two H5N1 live viruses of divergent strains. The above resultsdemonstrate that these two antibodies are effective against divergentstrains of IAVs. In addition, epitope analysis indicated that these MAbsexhibited strong reactivity against recombinant HA1 fusion proteinscontaining residues +3-322 (SEQ ID NO. 2), +3-259 (SEQ ID NO. 11),+28-259 (SEQ ID NO. 12), +45-259 (SEQ ID NO. 13), +72-259 (SEQ ID NO.14), as well as +72-115 (SEQ ID NO. 15), but had little to no reactivityagainst protein fragments covering residues +105-322 (SEQ ID NO. 9) and+105-259 (SEQ ID NO. 10). These results indicate that the neutralizingactivity may be mapped to residues +72-115 of H5N1 HA1. Amino acidsequence alignment of the HA1 region indicates that the +72-115 regionis highly conserved (>90% homology) among hundreds of strains of H5N1viruses causing human and non-human influenza infections, implying thatthe identified neutralizing MAbs recognized a highly conserved region ofIAV HA1. These results also demonstrated that the identifiedneutralizing MAbs had very low to no reactivity with overlappingpeptides covering the full-length HA indicated by low OD₄₅₀ valuesdetected by ELISA. The overlapping peptides have been known to be of alinear structure, without forming the native conformation of the HAstructure. In contrast, recombinant proteins expressing different HA1fragments of H5N1 virus fused with Fd and Fc, which were used for theabove antibody reactivity detection, maintain the native trimericstructure of the HA protein. However, when the conformation of these HA1fusion proteins were destroyed by denaturing reagent, such as DTT, theirreactivity with the two MAbs was decreased to a large extent. Thus, thefact that the MAbs had strong reactivity with native recombinant HA1proteins but low to no reactivity with DTT-treated denatured HA proteinsor overlapping peptides covering this region suggests that theidentified neutralizing MAbs recognized conformational structuressimilar to the native HA proteins of H5N1 virus.

Furthermore, the results demonstrated that both neutralizing MAbs (HA-3and HA-7) reacted strongly with HA1 proteins fused with theimmunoenhancer Fc of human IgG1 (HA1-hFc) (SEQ ID NO. 6), trimeric motiffoldon (Fd) sequences (HA1-Fd) (SEQ ID NO. 7), Fd plus Fc (HA1-Fd-hFc)(SEQ ID NO. 5) or HA1 protein alone (HA1-His) (SEQ ID NO. 8), but onlybackground or no reactivity with recombinant Fc of human IgG1 (hFc) (SEQID NO. 4), commercial human IgG (IgG-Fc), Fd control protein fused withHIV gp41 (HIV-Fd) and a control protein comprised of the receptorbinding domain (RBD) of SARS-CoV (SARS RBD), indicating that theneutralizing MAbs are highly specific to the HA1 protein of H5N1. Thisis in part due to the highly selective screening regimen (HA1-Hisprotein without Fd and Fc and inactivated H5N1 virus). Furtherexperimentation determined that both neutralizing antibodies are of theIgG1 subtype.

Further embodiments within the scope of this disclosure include methodsof preventing or treating influenza infections comprising administeringa therapeutically-effective or prophylactically effective amount of amonoclonal antibody having specificity for an epitope having at least90%, at least 92%, at least 95%, at least 97%, at least 98%, or at least99% homology to amino acids +72-115 of the HA1 domain of H5N1 influenzavirus hemagglutinin.

A pharmaceutical composition comprising the antibodies disclosed hereinincludes an acceptable carrier and is formulated into a suitable dosageform according to administration modes. Pharmaceutical preparationssuitable for administration modes are known, and generally includesurfactants that facilitate transport across the membrane. Suchsurfactants may be derived from steroids, or may be cationic lipids suchas N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride(DOTMA), or various compounds such as cholesterol hemisuccinate andphosphatidyl glycerol.

For oral administration, the pharmaceutical composition may be presentedas discrete units, for example, capsules or tablets; powders orgranules; solutions, syrups or suspensions (edible foam or whipformulations in aqueous or non-aqueous liquids); or emulsions.

For parenteral administration, the pharmaceutical composition mayinclude aqueous and non-aqueous sterile injection solutions which maycontain anti-oxidants, buffers, bacteriostats and solutes which renderthe formulation substantially isotonic with the blood of the intendedrecipient; and aqueous and non-aqueous sterile suspensions which mayinclude suspending agents and thickening agents. Excipients availablefor use in injectable solutions include, for example, water, alcohol,polyols, glycerin, and vegetable oils. Such a composition may bepresented in unit-dose (single dose) or multiple dose (several doses)containers, for example, sealed ampoules and vials, and may be stored ina freeze-dried (lyophilized) condition requiring only the addition ofthe sterile liquid carrier, for example water for injections,immediately prior to use. Extemporaneous injection solutions andsuspensions may be prepared from sterile powders, granules and tablets.

The pharmaceutical composition may include antiseptics, solubilizers,stabilizers, wetting agents, emulsifiers, sweeteners, colorants,odorants, salts, buffering agents, coating agents, or anti-oxidants.

If desired, the present composition, in addition to the antibody orantibodies, may contain a therapeutically active agent.

The present composition may be formulated into dosage forms for use inhumans or veterinary use.

In still another aspect, disclosed herein is a method of treatinginfluenza by administering the aforementioned antibodie(s).

The composition comprising the antibodie(s) may be administered toinfluenza-infected or highly susceptible humans and livestock, such ascows, horses, sheep, swine, goats, camels, and antelopes, in order toprevent or treat the incidence of influenza. When a subject is alreadyinfected, the present antibodie(s) may be administered alone or incombination with another antiviral treatment.

The antibody composition may be administered in a pharmaceuticallyeffective amount in a single- or multiple-dose. The pharmaceuticalcomposition may be administered via any of the common routes, as long asit is able to reach the desired tissue. Thus, the present compositionmay be administered via oral or parenteral (e.g., subcutaneous,intramuscular, intravenous, or intradermal administration) routes, andmay be formulated into various dosage forms. In one embodiment, theformulation is an injectable preparation. Intravenous, subcutaneous,intradermal, intramuscular and dropping injectable preparations arepossible.

The antibody composition may be administered in a pharmaceuticallyeffective amount. The term “pharmaceutically effective amount”, as usedherein, refers to an amount sufficient for treating or preventingdiseases, which is commensurate with a reasonable benefit/risk ratioapplicable for medical treatment or prevention. An effective dosageamount of the composition may be determined depending on the severity ofthe illness, drug activity, the patient's age, weight, health state,gender and drug sensitivity, administration routes, drugs used incombination with the composition; and other factors known in medicine,and may be readily determined by those skilled in the art. The antibodycomposition may be administered as a sole therapeutic agent or incombination with other therapeutic agents, and may be administeredsequentially or simultaneously with conventional therapeutic agents.This administration may be provided in single or multiple doses.

EXAMPLES Example 1 Generation of Monoclonal Antibodies

For the generation of MAbs specific to HA1, BALB/c mice weresubcutaneously immunized with a recombinant HA1-Fd-hFc protein (SEQ IDNO. 5) which comprised HA1 (residues +3-322 of H5N1 HA[A/Anhui/1/2005(H5N1)]) (SEQ ID NO. 2) fused with a trimeric Fd sequence(SEQ ID NO. 3) and an Fc immunoenhancer sequence (Fc of human IgG, hFc)(SEQ ID NO. 4) for four weeks at two week intervals. Three days afterthe last vaccination, the mice were sacrificed and the splenocytes fusedwith mouse myeloma cells (SP2/0). The hybridomas were screened by ELISAagainst an HA1-His protein (SEQ ID NO. 8) which comprised the same HA1region as the immunogen but was not fused to Fd or hFc. Clones which hadpositive results against HA1-His were also screened against inactivatedH5N1 virus of the homologous Anhui strain. Clones positive in both ELISAassays were then expanded, retested and subcloned to generate stablehybridoma cell lines. Twenty-five MAbs with high titer antibodyresponses were then screened for neutralizing activity against influenzavirus in a pseudovirus neutralization assay including HA proteins ofvarious isolates of influenza A viruses. The MAbs exhibitingneutralizing activity (HA-3 and HA-7) were then tested for passiveprotective immunity against two divergent strains of H5N1 virus. Inaddition, the MAbs were assayed by ELISA for specificity usingrecombinant HA1 proteins, or SARS RBD protein as controls. These twoMAbs were further tested by ELISA for reactivity with recombinantproteins containing different portions of the HA1 fusion protein(HA1-Fd-hFc) to determine the potential binding sites and map theepitopes of the MAbs. Furthermore, overlapping peptides covering thefull-length HA protein of A/Anhui/1/2005(H5N1) were also used as thetargets for the epitope mapping of the MAbs, as well as detection of theconformation of the MAbs. At last, the mechanism of these twoneutralizing MAbs was further analyzed using virus binding assay andpost-attachment assay.

Example 2 Virus Neutralization Assay and Protective Effects

Monoclonal antibodies (MAbs) HA-2, HA-3, HA-6, HA-7, HA-8, HA-9, HA-10,HA-11, HA-12, HA-13, HA-14, HA-15, HA-17, HA-18, HA-19, HA-20, HA-21,HA-22, HA-23, HA-24, HA-25, HA-27, HA-28, HA-29 and HA-30 were tested inthis assay.

An equal volume of H5N1 pseudovirus was added to wells containing theMAbs above and the plates incubated for 1 hr at 37° C. One hundredmicroliters of the virus/MAb mixture was then added to 293T cells plated6-8 hr previously. Fifty microliters fresh FBS-DMEM medium was added 24hr later and then luciferase activity was detected 72 hr later. H5N1pseudoviruses used for the test include XJ-HA, QH-HA, AH-HA, HK-HA, and1194-HA.

The protective potential of HA-3 and HA-7 MAbs against H5N1 influenzavirus infection was detected in mice. Six to eight week old femaleBALB/c mice were infected with 5 LD₅₀ (50% lethal dose) ofA/VietNam/1194/2004 (VN/1194, Glade 1) or A/Shenzhen/406H/06 (SZ/406H,Glade 2.3.4) H5N1 virus. Twenty-four hours later, the mice wereintravenously (i.v.) injected with 0.5 ml of purified MAbs containing 1mg of HA-3 or HA-7. The control group was given same amount of a MAbspecific to the RBD protein of SARS-CoV. Six infected mice per groupwere observed daily for 14 days to calculate the survival rate and bodyweight change. Six mice from each group were sacrificed on day 5post-treatment, and lung samples were collected for virologicaldetection.

A total of 25 MAbs selected from the fusion of HA1-Fd-hFcprotein-immunized mouse splenocytes were screened for neutralizingactivity by the pseudovirus H5N1 neutralization assay. Two antibodies(HA-3 and HA-7) exhibited high titers of neutralizing activity that notonly neutralized the homologous AH-HA strain but also neutralizedheterologous XJ-HA, QH-HA, HK-HA and 1194-HA strains (FIGS. 1-5).Importantly, both HA-3 and HA-7 were able to neutralize over 95% of theH5N1 pseudoviruses, including XJ-HA, QH-HA, AH-HA and HK-HA, at theconcentration as low as 0.7 mg/ml (FIG. 6).

All mice injected with HA-3 and HA-7 MAbs survived the infection withVN/1194 (Glade 1) (FIG. 7) and SZ/406H (Glade 2.3.4) (FIG. 8) H5N1virus, while no mice from the control group (injected with MAb againstRBD of SARS-CoV) survived infection with the above two viruses. Inaddition, no obvious body weight loss was observed in the mice immunizedwith HA-3 and HA-7 MAbs after infection with a lethal dose of VN/1194(FIG. 9) or SZ/406H (FIG. 10) H5N1 virus, while the mice in the controlgroup indicated continuous decrease of body weight, and none of themsurvived for over 10 days after infection with the virus. Observation ofthe viral titers in the infected mouse lung tissues indicated that noviral RNA was detectable in both HA-3 and HA-7-treated mice infectedwith VN/1194 and SZ/406H viruses, while a high level of viral RNA wasdetected in the control mice injected with the MAb specific to the RBDof SARS-CoV (FIG. 11). These results demonstrate that the two identifiedneutralizing MAbs HA-3 and HA-7 completely treated mice against lethalinfection with Glade 1 and Glade 2.3.4 strains of H5N1 virus, indicatingtheir use as passive immunotherapy for H5N1 virus infection.

Example 3 Specificity Detection and IgG Subtyping

ELISA plates were coated with the following purified proteins at aconcentration of 1 μg/ml at 50 μl/well in 0.1 M carbonate buffer (pH9.6): HA1-Fd-hFc (SEQ ID NO. 5), HA1-hFc (SEQ ID NO. 6), HA1-Fd (SEQ IDNO. 7), HA1-His (SEQ ID NO. 8), recombinant hIgG1-Fc2 protein (hFc) (SEQID NO. 4), commercial human IgG Fc protein (IgG-Fc) and foldon (Fd)fused with HIV-1 gp41 (HIV-Fd), as well as SARS RBD protein as controls.The plates were stored at 4° C. overnight to coat. The coated plateswere then blocked using 2% nonfat milk in phosphate-bufferedsaline/Tween (PBST) for 2 hr at 37° C. The MAb-containing supernatantswere diluted in sample buffer (1% nonfat milk) and incubated with thecoated plates at 50 μl/well for 1 hr at 37° C. The plates were thenwashed three times in PBST. Goat anti-mouse IgG HRP (1:2000), IgG1 HRP(1:2000), IgG2a HRP (1:5000), IgG2b HRP (1:2000) was added at 50 μl/wellfor 1 hr at 37° C. For IgG3 detection, a goat anti-mouse IgG3 (1:1000)was added at 50 μl/well for 1 hr at 37° C., the plates were washed andthen anti-goat HRP (1:5000) was added at 50 μl/well for 1 hr at 37° C.The plates were washed again and 50 μl/well3,3′,5,5′-tetramethylbenzidine (TMB) was added, followed by 25 μl/well1N H₂SO₄ to stop the reaction.

Both neutralizing MAbs (HA-3 and HA-7) reacted strongly with recombinantHA1 proteins fused with the hFc (IgG1) immunoenhancer (HA1-hFc) (SEQ IDNO. 6), the trimeric Fd sequences (HA1-Fd), or the Fd plus hFc(HA1-Fd-hFc), and HA1 protein without the hFc and Fd (HA1-His), but onlybackground levels of immunoreactivity were seen with hFc, IgG-Fc and therecombinant control proteins HIV-Fd and SARS RBD (FIG. 12). In addition,these two MAbs had strong reactivity with inactivated H5N1 virus, butlow to no reactivity with 2009 swine-origin influenza A virus (S-OIV)H1N1 and 2009/2010 seasonal influenza virus strains consisting of H1N1,H3N2 influenza A virus, and influenza B virus (FIG. 13). The aboveresults indicate that the selected MAbs are highly specific to the HA1protein of H5N1 virus. Both neutralizing MAbs were determined to be IgG1subtype (FIG. 14).

Example 4 Epitope Mapping

ELISA plates were coated with the following purified truncated HA1protein fragments at a concentration of 1 μg/ml at 50 μl/well in 0.1 Mcarbonate buffer (pH 9.6): HA+3-322 (HA1-Fd-hFc) (SEQ ID NO. 5),HA+105-322 (SEQ ID NO. 9), HA+105-259 (SEQ ID NO. 10), HA+3-259(HA-3-259) (SEQ ID NO. 11), HA+28-259 (SEQ ID NO. 12), HA+45-259 (SEQ IDNO. 13), HA+72-259 (SEQ ID NO. 14) and HA+72-115 (SEQ ID NO. 15). Theplates were stored at 4° C. overnight to coat. The coated plates werethen blocked using 2% nonfat milk in PBST for 2 hr at 37° C. TheMAb-containing supernatants were diluted in sample buffer (1% nonfatmilk) and incubated with the coated plates at 50 μl/well for 1 hr at 37°C. The plates were then washed three times in PBST. Goat anti-mousehorseradish peroxidase (HRP) at 1:2000 dilution was added at 50 μl/wellfor 1 hr at 37° C. The plates were washed again and 50 μl/well TMB wasadded, followed by 25 μl/well 1N H₂SO₄ to stop the reaction.

The ELISA data indicated that the two neutralizing MAbs (HA-3 and HA-7)reacted strongly with proteins covering the full-length HA1 of +3-322,and truncated HA1 fragments of +3-259, +28-259, +45-259, +72-259 and+72-115. However, these two MAbs had low to no reactivity with proteinscontaining HA+105-322 and HA+105-259 (FIG. 15). These results suggestthat the two neutralizing antibodies are specific for an epitope mappedto amino acids +72-115 (NVPEWSYIVEKANPANDLCYPGNFN DYEELKHLLSRINHFEKIQ,SEQ ID NO:15) of the HA1 region of H5N1.

Analysis of the epitope amino acid sequences indicated that the residues+72-115 region are highly conserved (>90% homology) among hundreds ofstrains of H5N1 viruses covering different clades that cause human andnon-human influenza infections.

The above HA1 proteins (SEQ ID NO. 5 and SEQ ID NO. 16-22) used forcoating the ELISA plates were expressed in mammalian 293T cells and werefused with the foldon (Fd) trimeric sequence and human IgG1 Fcimmunoenhancer, such that the proteins have the ability to maintain thenative conformational structure of the HA protein. Therefore the twoneutralizing MAbs can recognize the native conformation of the HAproteins.

Example 5 Reactivity to Overlapping Peptides and Denatured HA1 FusionProteins

ELISA plates were coated overnight at 4° C. with overlapping peptides(20 residues each overlapping 9 amino acid) covering the full-length HAprotein (SEQ ID NO. 1) of A/Anhui/1/2005(H5N1) at a concentration of 10μg/ml at 50 μl/well in 0.1 M carbonate buffer (pH 9.6), and then blockedusing 2% nonfat milk in PBST for 2 hr at 37° C. The MAbs were added tothe coated plates at 50 μl/well for 1 hr at 37° C. The plates were thenwashed three times in PBST. Goat anti-mouse HRP (1:2000) was added at 50μl/well for 1 hr at 37° C. The plates were washed again and 50 μl/wellTMB was added, followed by 25 μl/well 1N H₂SO₄ to stop the reaction.

To detect the reactivity of MAbs HA-3 and HA-7 with denatured HA1proteins, ELISA plates were coated with recombinant HA1 proteins at 1μg/ml overnight at 4° C. Then the coated plates were treated with DTT(final concentration 10 mM) for 1 hr at 37° C., followed by washes withPBST. Then the wells were treated with 50 mM iodoacetamide for 1 hr at37° C. After washing with PBST, ELISA was performed as above.

Neutralizing MAbs HA-3 and HA-7 had very low reactivity with overlappingpeptides covering the full-length HA proteins of H5N1 (FIGS. 16A-C).These peptides were linear and did not form the native three-dimensionalconformation of the HA structure. Similarly, the reactivity of MAbs HA-3and HA-7 with DTT-treated HA1 fusion proteins decreased significantly,although these MAbs have strong reactivity with native forms of HA1proteins (FIG. 17).

The fact that MAbs HA-3 and HA-7 had a strong reaction with recombinantproteins encompassing different fragments (covering +72-115 amino acids)of the HA1 of H5N1 with Fd and Fc (FIG. 17) but have little to noreactivity with denatured HA1 proteins (FIG. 17) or overlapping peptidescovering this region (FIG. 16) indicates that the identifiedneutralizing MAbs recognize conformational structures similar to nativeHA proteins rather than linear structures.

Example 6 Mechanism of Inhibition by MAbs

Virus binding assays were performed using the QH-HA H5N1 pseudovirus.The virus was incubated with serial diluted MAbs HA-3 and HA-7 or IgG-Fccontrol antibody in DMEM containing 1% BSA at 4° C. overnight. MDCKcells were seeded in 96-well plates 24 hr before infection and blockedwith DMEM containing 1% BSA (100 μl/well) at 4° C. for 1 hr. The mixtureof virus and MAbs was then added to MDCK cells at 4° C. for 2 hr. Cellswere then washed four times with PBS containing 1% BSA to remove unboundvirus. The lysed cells were quantified for HIV p24 content by ELISA.Percentage of viral binding was expressed as relative percentage of thep24 reading from the cells without the antibodies (No MAb), which wasset as 100%.

A post-attachment assay was performed using the QH-HA H5N1 pseudovirus.The virus was added to MDCK cells plated 18 hr before test, andincubated at 4° C. for 6 hr. After washing the cells three times withcold PBS to remove unbound virus, serially diluted MAbs HA-3 and HA-7,as well as control antibodies to SARS RBD and IgG-Fc, were added to theMDCK monolayer for 2 hr at 4° C. Fresh DMEM was added to the monolayerand cells were incubated at 37° C. Luciferase activity of the cells wasthen measured 72 hr post-infection. Percentage of viral entry wasexpressed as relative percentage of the luciferase reading from thecells without the antibodies (No Ab), which was set as 100% (% viralentry=luciferase reading of Abs/No Ab*100%).

Results from the virus binding assay showed that increasing theconcentration of the two neutralizing MAbs did not decrease the bindingof the virus to MDCK cells, which were similar to those from thenegative control human IgG Fc (FIG. 18). These results suggest that theinhibition of H5N1 viruses by MAbs HA-3 and HA-7 is not through theprocess of blocking the receptor binding.

A post-attachment assay was further performed to characterize themechanism of these two MAbs. Results depicted in FIGS. 19 and 20indicates that both HA-3 and HA-7 inhibited the post-attachmentprocesses in a dose-dependant manner, while the negative controls Abs(SARS RBD and human IgG-Fc) did not neutralize virus entry even at thehighest concentration of 10 μg/ml, confirming that MAbs HA-3 and HA-7inhibited virus entry at the post-attachment process rather than thereceptor binding process.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about”. Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe specification and attached claims are approximations that may varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques. Notwithstanding that the numerical ranges and parameterssetting forth the broad scope of the invention are approximations, thenumerical values set forth in the specific examples are reported asprecisely as possible. Any numerical value, however, inherently containscertain errors necessarily resulting from the standard deviation foundin their respective testing measurements.

The terms “a,” “an,” “the” and similar referents used in the context ofdescribing the invention (especially in the context of the followingclaims) are to be construed to cover both the singular and the plural,unless otherwise indicated herein or clearly contradicted by context.Recitation of ranges of values herein is merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range. Unless otherwise indicated herein, eachindividual value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein isintended merely to better illuminate the invention and does not pose alimitation on the scope of the invention otherwise claimed. No languagein the specification should be construed as indicating any non-claimedelement essential to the practice of the invention.

Groupings of alternative elements or embodiments of the inventiondisclosed herein are not to be construed as limitations. Each groupmember may be referred to and claimed individually or in any combinationwith other members of the group or other elements found herein. It isanticipated that one or more members of a group may be included in, ordeleted from, a group for reasons of convenience and/or patentability.When any such inclusion or deletion occurs, the specification is deemedto contain the group as modified thus fulfilling the written descriptionof all Markush groups used in the appended claims.

Certain embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention. Ofcourse, variations on these described embodiments will become apparentto those of ordinary skill in the art upon reading the foregoingdescription. The inventor expects skilled artisans to employ suchvariations as appropriate, and the inventors intend for the invention tobe practiced otherwise than specifically described herein. Accordingly,this invention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

Specific embodiments disclosed herein may be further limited in theclaims using consisting of or consisting essentially of language. Whenused in the claims, whether as filed or added per amendment, thetransition term “consisting of” excludes any element, step, oringredient not specified in the claims. The transition term “consistingessentially of” limits the scope of a claim to the specified materialsor steps and those that do not materially affect the basic and novelcharacteristic(s). Embodiments of the invention so claimed areinherently or expressly described and enabled herein.

Furthermore, numerous references have been made to patents and printedpublications throughout this specification. Each of the above-citedreferences and printed publications are individually incorporated hereinby reference in their entirety.

In closing, it is to be understood that the embodiments of the inventiondisclosed herein are illustrative of the principles of the presentinvention. Other modifications that may be employed are within the scopeof the invention. Thus, by way of example, but not of limitation,alternative configurations of the present invention may be utilized inaccordance with the teachings herein. Accordingly, the present inventionis not limited to that precisely as shown and described.

What is claimed is:
 1. A neutralizing monoclonal antibody specificallybinding an epitope of the HA1 domain of H5N1 influenza virushemagglutinin, the epitope having an amino acid sequence of SEQ IDNO:15, wherein the antibody is produced by hybridoma HA-3 having ATCCaccession number PTA-12174 or hybridoma HA-7 having ATCC accessionnumber PTA-12173.
 2. The neutralizing monoclonal antibody of claim 1wherein said antibody is a mouse antibody.
 3. The neutralizingmonoclonal antibody of claim 1 wherein said antibody is anantigen-binding fragment which binds to SEQ ID NO:15.
 4. Apharmaceutical formulation for neutralizing influenza virus comprising amonoclonal antibody according to claim
 1. 5. The pharmaceuticalformulation of claim 4 wherein said formulation further comprises atleast one pharmaceutically acceptable excipient.
 6. A method of treatinginfluenza virus infection in a subject in need thereof comprisingadministering a therapeutically effective amount of the neutralizingmonoclonal antibody of claim 1 and thereby treating said influenza virusinfection in said subject.